1. Field of the Invention
The invention relates to a substrate cutting method and a substrate cutting apparatus. More particularly, for example, the invention relates to a substrate cutting method and a substrate cutting apparatus which are suitably used for cutting a substrate of a thin film semiconductor device constructed by adjacently arranging substantially in a plane a plurality of substrates on each of which thin film semiconductor elements which are two-dimensionally arranged are installed.
2. Related Background Art
A reduction optical system and a CCD type sensor are generally used as a reading system of a facsimile, a digital copying apparatus, an X-ray image pickup apparatus, or the like. In recent years, however, owing to the development of a photoelectric converting semiconductor material represented by amorphous silicon hydride (hereinafter, abbreviated to “a-Si”), what is called a one-dimensional or two-dimensional contact type sensor such that photoelectric converting elements and a signal processing unit are formed on a substrate of a large area and an image is read by an optical system having the same magnification as that of an information source is progressively being developed. Particularly, since a-Si can be used as not only a photoelectric converting material but also a thin film electric field effect type transistor (hereinafter, abbreviated to “TFT”), a-Si has an advantage such that a photoelectric converting semiconductor layer and a semiconductor layer of the TFT can be simultaneously formed.
As an example of a photoelectric converting apparatus having such a contact type sensor, we have proposed an apparatus disclosed in the Official Gazette of European Patent Publication Laid-Open No. 0660421.
FIG. 1 is a schematic overall circuit diagram showing an example of the foregoing photoelectric converting apparatus. FIG. 2A is a schematic plan view for explaining an example of an element which is used as each component element corresponding to one pixel of the above photoelectric converting apparatus. FIG. 2B is a schematic cross-sectional view taken along the line 2B—2B in FIG. 2A.
In FIG. 1, S11 to S33 denote photoelectric converting elements. One electrode side of such an element (for example, a lower electrode side) is shown by G and another electrode side (for example, an upper electrode side) is shown by D. C11 to C33 denote capacitors for accumulation; T11 to T33 TFTs for transfer; Vs a power source for reading out; and Vg a power source for refreshing. The power sources Vs and Vg are respectively connected to the G electrodes of all of the photoelectric converting elements S11 to S33 through switches SWs and SWg. The switch SWs is connected to a refresh control circuit RF through an inverter. The switch SWg is directly connected to the refresh control circuit RF and is controlled so as to be turned on for a refreshing period of time. One pixel is constructed by one photoelectric converting element, a capacitor, and a TFT and its signal output is connected to an integrated circuit IC for detection by a signal wiring SIG.
According to the photoelectric converting apparatus which has been proposed by us before, a total of nine pixels are divided into three blocks and outputs of three pixels per block are simultaneously transferred and are sequentially converted into outputs by the integrated circuit IC for detection through the signal wiring SIG and are generated (Vout). Three pixels in one block are arranged in the lateral direction and three blocks are sequentially vertically arranged, thereby two-dimensionally arranging the pixels.
Although a portion surrounded by a broken line in the diagram is formed on a same insulating substrate of a large area, a schematic plan view of an example of a portion corresponding to the first pixel in such a large area portion is shown in FIG. 2A. A schematic cross-sectional view of a portion taken along a broken line 2B—2B in FIG. 2A is shown in FIG. 2B. As for the photoelectric converting element S11, TFT . . . T11, and accumulating capacitor C11, the elements are not particularly separated but the capacitor C11 is formed by increasing an area of an electrode of the photoelectric converting element S11. Such a structure can be accomplished because the photoelectric converting element and the capacitor has the same layer construction.
A silicon nitride film SiN for passivation and a fluorescent material such as cesium iodide CsI or the like serving as a wavelength converting material are formed in the upper portion of the pixel. In such a structure, when an X-ray enters from the upper position, it is converted into light (shown by a broken line arrow) by the fluorescent material CsI and the light enters the photoelectric converting element. In the photoelectric converting apparatus, as shown in the diagram, nine pixels are two-dimensionally arranged in a form of 3×3. As will be also understood from the diagrams with respect to the driving, an example in which the outputs of the nine pixels are divisionally transferred and generated three times simultaneously for every three pixels is shown. Therefore, by two-dimensionally arranging the pixels as, for example, (5×5) pixels per millimeter in the vertical and lateral directions, an X-ray detector of (40 cm×40 cm) is derived. By combining such an X-ray detector to an X-ray generator in place of an X-ray film and constructing an X-ray Roentgen apparatus, such an apparatus can be used for a nondestructive inspection of a structural material or the like, such as performing a chest Roentgen medical examination, or examining for cancer of the breast. Different from the film, consequently, an output of such an apparatus can be instantaneously displayed by a CRT. Further, the output also can be converted into an output according to an object by converting the output into a digital value and performing image processing by a computer. The output also can be stored onto a magnetooptic disk and a past image also can be instantaneously retrieved. As for a sensitivity as well, a clear image can be obtained by a very weak X-ray in which an influence on the human body is less than that by the film.
FIGS. 3 and 4 are schematic plan views showing embodiments of a photoelectric converting apparatus having (2000×2000) pixels as examples. In the case of constructing (2000×2000) detectors, it is sufficient to increase the number of elements in a region surrounded by the broken line shown in FIG. 1 in the vertical and lateral directions. In this case, however, there are 2000 control wirings g1 to g2000 and there are also 2000 signal wirings SIG (sig1 to sig2000). A shift register SR1 and the integrated circuit IC for detection also have to execute 2000 control processes, so that a scale of the apparatus is large.
In a photoelectric converting apparatus of a large area in which the substrate area increases and the number of elements which are formed increases, it is difficult to perfectly eliminate micro dust upon manufacturing, particularly, debris which is peeled off from a wall of a thin film depositing apparatus when an amorphous silicon layer is deposited onto the substrate and dust remaining on the substrate when a metal layer is deposited onto the substrate. There is, consequently, a case where it is not easy to eliminate an inconvenience of the wirings, namely, a short-circuit or an open state of the wirings.
When the control wiring or signal wiring of the photoelectric converting apparatus is short-circuited or opened, there is a case where output signals of all of the photoelectric converting elements connected to such a wiring are inaccurate. In such a case, the apparatus cannot be actually used as a photoelectric converting apparatus. Namely, as one sheet of a substrate when the photoelectric converting apparatus of a large area is manufactured enlarges in size, a probability of the occurrence of the short-circuit or open state per substrate rises. Thus, a yield of the substrate decreases with an increase in size of the substrate and, at the same time, an amount of loss due to an inconvenience per substrate also increases.
To solve the above problems, a method of constructing a larger effective area by adjacently arranging as if in a plane a plurality of substrates on each of which photoelectric converting elements which are two-dimensionally arranged are installed has been proposed.
A proposed structure will now be described with reference to the drawings.
In a photoelectric converting apparatus shown in FIG. 5, it is a characteristic point that four photoelectric converting apparatuses 100, 200, 300, and 400 constructed on four substrates are joined substantially in a plane (adjacently arranged), thereby constructing one large photoelectric converting apparatus.
For instance, (100×100) photoelectric converting elements are arranged on the photoelectric converting apparatus 100 and are connected to a total of 2000 wirings of the 1000 control wirings g1 to g1000 and the 1000 signal wirings sig1 to sig1000. The shift register SR1 is formed in one chip every 100 stages. Ten shift registers SR1-1 to SR1-10 are arranged on the substrate 100 and are connected to the control wirings g1 to g1000.
The integrated circuit for detection is also formed in one chip every 100 processing circuits. Ten integrated circuits IC1 to IC10 are arranged and are connected to the signal wirings sig1 to sig1000. Even in the photoelectric converting apparatuses 200, 300, and 400, in a manner similar to the photoelectric converting apparatus 100, (100×100) photoelectric converting elements are arranged and are connected to 1000 control wirings by 1000 signal wirings. In addition, ten shift registers and ten integrated circuits for detection are arranged, thereby constructing a large photoelectric converting apparatus.
As a method of cutting each substrate of the photoelectric converting apparatuses 100, 200, 300, and 400 so as to obtain design dimensional values, a slice line is formed on the substrate on which the photoelectric converting elements are installed and the slice line is cut, thereby cutting each substrate.
Ordinarily, a cutting apparatus is constructed by a stage to hold the substrate and a blade as a cutting member. The stage can be moved in the X-axis direction (left/right direction on the paper surface) and can be rotated. The blade can be moved in the Y-axis direction (upper/lower direction on the paper surface; the rotation of the blade is parallel with the X direction). Thus, four sides of the substrate can be cut. Specifically speaking, the blade is moved in the Y-axis direction to the cutting position. The stage is rotated and a rotary axis is fixed in a manner such that the slice line which is used as an alignment mark displayed on the monitor screen through a camera fixed to a blade unit is parallel with the slice direction, namely, a stage moving direction. After that, the stage and blade are moved to a cutting start position and the blade is dropped onto the substrate, thereby starting the cutting operation. The cutting is executed by mechanically moving the stage in the X direction. After four sides were cut as mentioned above, four substrates are combined and joined substantially in a plane onto the substrate so as to form a gap between the adjacent substrates, thereby forming the photoelectric converting apparatus of a large area.
According to the photoelectric converting apparatus with the above construction, by improving a yield per substrate upon manufacturing, costs of the substrate are reduced, so that the costs of the photoelectric converting apparatus of a large area or in which a plurality of substrates are combined can be reduced.
However, in the foregoing photoelectric converting apparatus of a large area constructed by joining substantially in a plane a plurality of substrates on each of which the photoelectric converting elements which are two-dimensionally arranged are installed, when the cut substrates are arranged, the gap between the substrates is not constant, so that there is a subject to be improved such that there is a case where an image quality of the gap portion of the photoelectric converting apparatus of the large area deteriorates.
FIG. 6A is a schematic plan view showing a positional misalignment or a bending of the cut line 111 at the time of such a substrate cutting. Reference numeral 101 denotes a slice line and 103 indicates a photoelectric converting portion of a unit of one substrate. As shown in FIG. 6A, a state in which a positional misalignment or a bending of the cut line 111 occurs due to a position matching or parallel ejection misalignment or a precision of the apparatus is illustrated.
FIG. 6B is a diagram clearly showing a variation in gaps between the substrates in the case where four substrates (photoelectric converting portions) 103 each having a cutting position misalignment or a bending of the cut line as mentioned above are arranged on a base plate 105. As shown in FIG. 6B, there is a case where a gap occurs between the adjacent substrates upon joining due to a misalignment, a bending, or a warp of the cut surface. Although the conventional apparatus obviously does not have such a large misalignment or bending, it is a fact that there is also a case where a problem occurs from a viewpoint of a size of a pixel.